A systematic review on MEG and its use in the presurgical evaluation of localization-related epilepsy

Lau M, Yam D, Burneo JG

CRD summary

This review found insufficient evidence to support the relationship between use of MEG in surgical planning and seizure-free outcome after epilepsy surgery. A number of methodological flaws and the questionable appropriateness of the outcome measures used mean that the reliability of the results is unknown.

Authors' objectives

To determine the effectiveness of magnetoencephalography (MEG) in the pre-surgical evaluation of localization-related epilepsies.

Searching

MEDLINE, EMBASE and The Cochrane Library were searched for relevant English-language studies from 1987 to 2006; search terms were reported. References of original articles, reviews abstracts and book chapters were searched in November 2006 to identify additional articles. The reviewers contacted experts on MEG and epilepsy to source further unpublished studies.

Study selection

Original studies of four or more patients who underwent resective or non-resective surgery for epilepsy in which MEG was used pre-operatively to determine the epileptogenic focus area were eligible for inclusion. Additional inclusion criteria were that outcomes of seizure frequency or seizure-free time as defined by the study authors were to be reported after a minimum follow-up of six months post-surgery and that MEG focus was compared quantitatively to the resected or operated area.

Patients in the included studies were diagnosed with extra-temporal and/or temporal epilepsy. Patient age ranged from four to 68 years. Most patients underwent resective surgery; some also underwent multiple subpial transection. Most studies used Engel's classification to define seizure outcomes; one study used Wiesner's new classification. Some studies used additional diagnostic tools.

Two authors independently performed the study selection.

Assessment of study quality

The authors did not state that they assessed methodological quality.

Data extraction

Two reviewers independently extracted data to create 2x2 tables that compared concordance and freedom from seizures to calculate sensitivity, specificity and positive and negative likelihood ratios for each of the studies Indeterminate or zero values were excluded. MEG epileptogenic localisation was considered concordant to the resected area if there was partial or complete overlap of more than 60%. Any disagreements between the authors were resolved by discussion with a third reviewer.

Seventeen studies were included in the review (n=244). Sample sizes in the included studies ranged from four to 41 patients. The percentage of concordant and patients who were seizure-free at follow-up ranged from 12% to 100%.

There was insufficient evidence in the literature to support the relationship between use of MEG in surgical planning and seizure-free outcome after epilepsy surgery. Additional controlled and consistent studies were required to determine whether MEG was an adequate replacement as a diagnostic tool for EEG.

CRD commentary

The review addressed a clear objective and criteria for study inclusion were stipulated. Appropriate electronic databases were searched. Attempts were made to identify unpublished studies. The restriction to English-language studies meant that there was a risk of language bias. Steps were taken to minimise errors and bias for study selection and data extraction. No quality assessment was undertaken, so the reliability of the results was unclear. The authors stated that the studies were heterogeneous with respect to MEG analysis, patient populations and epilepsy type. The authors used mean confidence intervals to report results, which did not provide additional information on the robustness of the results. Therefore, statistical pooling of the study results may not have been appropriate, particularly given the use of additional diagnostic tools and inclusion of patients who underwent multiple subpial transection. It was unclear to what extent use of seizure outcome post-resective surgery was an appropriate outcome measure to confirm the accuracy of MEG as a diagnostic tool. The authors correctly stated limitations of the review in terms of small study samples and multiple sources of variation across the studies.

Methodological flaws and uncertainty about the comparisons made and use of outcome measures mean that the authors conclusions should be interpreted with caution and the reliability of the results is unknown.

Implications of the review for practice and research

Practice: The authors did not state any implications for practice.

Research: The authors stated that more controlled and consistent studies were required to determine whether MEG was an adequate replacement as a diagnostic tool for EEG.

Funding

None stated.

Bibliographic details

Lau M, Yam D, Burneo JG. A systematic review on MEG and its use in the presurgical evaluation of localization-related epilepsy. Epilepsy Research 2008; 79(2-3): 97-104

This is a critical abstract of a systematic review that meets the criteria for inclusion on DARE. Each critical abstract contains a brief summary of the review methods, results and conclusions followed by a detailed critical assessment on the reliability of the review and the conclusions drawn.